The present invention relates to an electron beam lithography, and more particularly, to an improvement in the accuracy of the connecting portion of patterns joining together, which are delineated by using a high current density electron beam such as that employed in a high throughput electron beam lithography.
High throughput electron beam (EB) lithography is becoming indispensable to facilitate quick turnaround in the fabrication of a variety of VLSI (very large scale integration) semiconductor circuits. In such high throughput EB lithography for VLSI circuits a relatively high current density and high energy electron beam is used. For instance, the current and acceleration energy of an electron beam employed in high throughput EB lithography are greater than 1 microampere (uA) and 20-80KeV, respectively, which are relatively larger than the current of few to hundreds of nanoamperes (nA) and the acceleration energy of 20KeV or less in a conventional EB lithography.
On the other hand, there occurs a problem relating to a faulty connection of patterns which are formed to join together through the respective predetermined edge portions thereof, when the patterns are delineated by using a high throughput EB lithography. Such faulty connection is generally caused by the narrowing in the pattern width occurring in the vicinity of the respective edge portions of the patterns to be joined. The narrowing would not only decrease the accuracy of a composite pattern formed from the joined patterns but also result in the disconnection inherent in the composite pattern. If the composite pattern constitutes an interconnecting wiring line, such faulty connection would produce a wiring of an insufficient current capacity or an open-circuited interconnection.
According to a study on the faulty connection between the patterns delineated by a high throughput EB lithography, it is revealed that the above-mentioned narrowing in the width of a pattern is caused in association with the temperature dependency of the sensitivity of the resist material layer involved therein and is enhanced with the increase in the time interval between the formation of the patterns to be joined together. Accordingly, it is requested to provide a method of an EB exposure for forming patterns regardless of the temperature dependency of the resist material and of the influence of such time interval, while the development of an electron beam sensitive resist material having a sensitivity characteristic with less temperature dependency is going to be undertaken.